Our team at Pearmill has seen a lot of Google Ads accounts over the years: fintech giants, scrappy DTC brands, marketplaces, you name it. And almost every time we sit down with a leadership team, it feels like the same quiet worry is in the room, even when no one wants to say it out loud: are these conversions even real?

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We get why that question is uncomfortable. Most marketers are stretched thin, the dashboard says the CPA looks good, and the pressure to keep spend efficient is relentless. It's easier to take Google's numbers at face value and keep moving. We've been there, both as operators and as a team helping clients out of it.

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But here's the truth our paid search team keeps coming back to: every dollar in performance marketing carries a question that should keep you up at night. Did the ad actually cause this conversion, or would the customer have come anyway?

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That is the question of incrementality. It's arguably the most important question in performance marketing today, and it's also one of the hardest to face honestly.

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This is Part 1 of a three-part series where we'll help you discover if your paid search ads are actually causing conversions, or just claiming credit for them.

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• Part 1 we’re talking about what incrementality actually means, and two ways to measure it.
• Part 2 covers the test that produced our most counterintuitive finding.
• Part 3 gets into what you actually do with the numbers.

On August 12th, Het is going live to walk through all of it and take your questions. Register for the webinar here →

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What platforms tell you vs. what's true

Google's attribution, whether you're on last-click or data-driven, measures correlation, not causation. It tells you which ad a user touched before converting. It doesn't tell you whether the ad changed their behavior. That's not Google being sneaky. It's just what platform attribution is built to do.

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The gap between attributed performance and incremental performance is rarely small, and that's the part that catches teams off guard. One of our DTC clients recently ran a year-long incrementality program on their own paid search account, with four independent experiments. The answer wasn't subtle, and honestly, it wasn't an easy conversation to walk into.

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The number that matters is the incrementality factor:

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Incrementality Factor = Absolute Lift / Attributed Conversions

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If that number is 60%, then for every 100 conversions Google claims credit for, only 60 actually wouldn't have happened without the ad. The other 40 were going to convert through organic, direct, brand recall, or another channel anyway. You're paying retail for inventory you already owned. That's not a knock on your team. It's the default state of most accounts we've ever worked with, ours included before we saw the data.

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The companion metric is iCPA (Incremental CPA), calculated as Total Spend / Incremental Conversions. It's always higher than what the platform reports, sometimes meaningfully so. For our DTC client, the iCPA on Non-Brand Search came in roughly 68% higher than what Google was showing in the dashboard. That's not a rounding error. That's the difference between scaling and burning. And once we walked the team through the data, the conversation got a lot more productive.

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So the question stops being philosophical and becomes practical: how do you actually measure the real number? There are four ways to do it, each with its own blind spots. That's where we're headed next.

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Stay tuned and join us for our Webinar on August 12th, for all your incrementality questions. Register for the webinar here →

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